There have recently been developed engines for motor vehicles comprising a timing belt having an oil wet belt and capable of meeting at least the same durability requirements as dry belt drives or chain drives. It is specified that the expression “oil wet” used in the description and in the claims refers both to applications in which the belt is at least partially immersed in oil at rest and to applications in which the oil is conveyed on the belt, e.g. by spraying by means of a specific nozzle or by splashing due to the action of the belt or the pulleys.
Specifically, the environment in which the belt drive of the present invention works may be the same as that in which a chain drive works.
With respect to chain drives, belt drives present lower costs and much lower loss due to friction. Furthermore, a belt drive is less noisy and the elongation of the belt is lower by at least one fourth with respect to that of a chain: this allows to more precisely control the internal combustion engine valves.
A chain drive generally comprises a tensioning device for guaranteeing the correct operation of the belt.
As the belt is oil wet, it may be tensioned by means of a shoe operated by an actuator. The shoes have the advantage of being mountable in small spaces and thus of making the drive compact. In this manner, the belt drive is interchangeable with a chain drive without having to modify the compartment which accommodates the drive.
However, a shoe having a non-optimised longitudinal profile causes an increase of power dissipated by friction against the belt and the subsequent temperature increase deteriorates the belt and reduces the active working life thereof.